Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia, characterised by the accumulation of immuno-incompetent, monoclonal CD5+ B-lymphocytes. CLL has a very heterogeneous clinical course with survival ranging from a few months to many decades. Treatment strategies vary with staging and disease progression and include chemotherapy, radiotherapy, monoclonal antibody therapy or bone marrow transplantation, with early stage patients often receiving no treatment. Early clinical intervention is required for patients with an aggressive form of the disease, whereas patients with more benign forms simply need monitoring for disease progression at which point appropriate treatment may be administered. In this latter respect, it has been shown that early stage CLL intervention does not improve survival rates. It is therefore inappropriate to expose someone presenting with a disease that is unlikely to be life-threatening for up to 30 years with highly dangerous chemotherapeutic drugs. A reliable method for distinguishing the various forms of the disease is therefore desirable. Although the Binet and Rai staging systems are reliable predictors of clinical outcome between the staging groups, they fail to identify good and poor prognostic subsets within each stage. Since most patients present with early stage disease at diagnosis, a number of laboratory tests have been developed to try and predict the clinical course of these patients, most notably, immunoglobulin variable heavy chain somatic mutation status, CD38 expression, T-cell tyrosine kinase (ZAP-70) expression and cytogenetic abnormalities. Unmutated IGHV genes, high CD38 expression, high ZAP-70 expression and the presence of 17p and 11q deletions are all associated with a poor prognosis. The exploitation of this sort of laboratory data to provide a prognostic assay is described in US 2008/0026383. However, none of these individual markers can provide definitive prognostic information alone and when used in combination offer only a reasonable prognostic prediction.
Breast cancer is another very common tumour type in the western world. Breast tumours can be surgically removed but remnants of the tumour can remain resulting in the reoccurrence of the disease. Patients therefore have adjuvant treatments that have toxic side effects, and the suspicion is that many patients receive treatment that will not be beneficial to them. The usual approach is to tailor the aggressiveness of the chemotherapy to the risk of recurrence. As compared with standard chemotherapy, aggressive chemotherapy is associated with a greater benefit, but also with more acute and long-term toxic effects such as leukaemia and heart failure. As with CLL, there is thus a requirement for markers that allow prognostication following surgery for breast cancer. Gene expression arrays have been employed to identify specific gene expression signatures that are indicative of prognosis; these provide hazard ratios of up to 3.4 for overall survival in node negative breast cancer patients. Gene expression arrays are amongst the best markers of prognostication currently available for Breast cancer.
Myelodysplastic syndromes (MDS) are a heterogeneous collection of disorders of the bone marrow haematopoietic stem cells characterised by disruption to haematopoiesis ultimately leading to bone marrow failure. This condition was previously known as ‘pre-leukaemia’ because one third of patients progress to acute myeloid leukaemia (AML). There is therefore a clinical need to distinguish patients that progress to AML, and thus may require therapy from those that manifest a more benign form of the disease. Like CLL, MDS is characterised by large-scale unbalanced chromosomal rearrangements; these types of rearrangements are consistent with telomere dysfunction. Furthermore, there is evidence of telomere erosion in MDS and that mutation in the telomerase RNA components can confer MDS in children.
It follows from the above, that there is a range of diseases for which relatively early stage prognostication would be advantageous. Moreover, many of these diseases are characterised by genetic abnormalities and, specifically telomere shortening. These diseases include alzheimer's disease1, brain infarction1, heart disease1, chronic HIV infection1, chronic hepatitis1, skin diseases1, chronic inflammatory bowel disese1 including ulcerative colitis, anaemia1, atherosclerosis1, Barrett's oesophagus and cancers1 including pre-cancerous conditions. The disclosure therefore has application to all of these diseases.
Telomeres are nucleoprotein structures composed of repetitive DNA sequences that cap the ends of linear eukaryotic chromosomes, protecting them from deterioration or fusion with adjacent chromosomes. During replication of DNA, the ends of chromosomes cannot be processed, and as a result during cell division the chromosome ends would be lost; telomeres however prevent this by themselves being consumed during each stage of cell division, essentially ‘capping’ the chromosome. Telomere ends are, however, maintained in certain cell types such as germ cells, stem cells and certain white blood cells, by the reverse transcriptase telomerase that catalyses the RNA templated addition of telomere repeats. Telomere length is a key determinant of telomeric function and it has been shown that short dysfunctional telomeres can drive genomic instability and tumourigenesis in mouse models. Furthermore, deregulation of telomerase has been shown to drive oncogenesis. Additionally, the loss of telomeres in somatic cells has been linked to replicative senescence preventing genomic instability and cancer. Conversely, it has also been shown that malignant cells can bypass this senescence and become immortalised by telomere extension by aberrant activation of telomerase.